Very broad molecular weight distribution (MWD) resins can be efficiently produced in tubular, high pressure reactors by feeding all fresh ethylene (which is achieved through the lining-up of the primary compressor system to the secondary compressor system) to the front of the reactor. However, a very low or zero chain transfer agent (CTA) concentration fed to the front of the reactor can result in high gel levels (GI 200) as well as reactor fouling.
Reactor fouling and/or gel-formation in the product can happen instantaneous and/or delayed and both phenomena are thought to be related to each other. For instance formation of ultra-high molecular weight can lead to deposition of this polymer at the reactor wall or at the walls of the separator. This deposition in the reactor leads to fouling and reduced heat transfer. Removal of this deposited polymer in the reactor and/or separator can happen in a continuous manner during the production of this polymer, delayed until after the production of this polymer and/or in a non-continuous manner resulting in gel showers. The removal will improve heat transfer in the reactor, but it will also result in a temporarily higher and/or unacceptable gel-level in the product.
WO 2012/117039 (Basell 2012) describes fresh ethylene lineup to the front of the reactor to broaden the MWD of the resin. Less than 70% of the concentration in the reaction zones where the highest CTA concentration are injected/consumed.
U.S. Pat. No. 3,334,081 (Union Carbide; 1960) describes a tubular reactor with at least two separate feed streams, where the chain transfer agent is injected via the inlet as a mixture with ethylene and or is introduced in a side stream undiluted or as a mixture with ethylene.
U.S. Pat. No. 3,917,577 (BASF; 1975) describes a variation in CTA feed split to achieve a relatively narrow MWD resin.
DD 276 598 A3 (Leuna; 1988) describes a flexible line up of primary compressors to control oxygen levels in ethylene feed streams that resulted in very limited variation in CTA levels. The same line up, described in FIG. 2, without oxygen as initiator could be used to enhance distribution of CTA.
U.S. Pat. No. 9,120,880 describes a polymerization process with fresh ethylene distributions for preparation of low density ethylene-based polymers.